This invention relates to polymer films having a fine grid of hand tear lines permitting sizing of the film by hand in more than one direction without the use of cutting tools.
Our U.S. Pat. No. 4,298,647 and the related application U.S. Ser. No. 290,354 now U.S. Pat. No. 4,380,569, resulted from an investigation under-taken to develop a plastic film or sheet material which could be sized by hand without the use of cutting tools in both a lengthwise and widthwise direction to quickly and easily conform it to the surface which it is to cover. That investigation was directed particularly to developing a decorative plastic covering material which could be used, for example, as a shelf liner. In the course of that investigation, a sheet material which tore easily and cleanly in both directions with generally the same degree of tearing force but which also had good tensile strength in both its lengthwise and widthwise direction to be able to withstand normal handling during both fabrication and use without unintentional tearing of the material was developed. This material has been in the marketplace and has been commercially successful. During the course of further development work, it was recognized that there existed a further need for plastic films having the same desirable properties but for uses other than the decorative covering of a surface. Examples of such applications are in the medical field wherein there is a need for hand-sizable plastic tape with adhesive on one side thereof whereby medical personnel simply can tear off a piece of adhesive tape of exactly the desired length and width to suit the particular need. Another application would be in the formation of hand-tearable films such as may be useful for providing the film for a hand-sizable window shade. Surprisingly, we have discovered that the present invention is handtearable through a heat seal further adding to its usefulness as a window shade film.
In the development of the decorative shelf liner, the size of the grid of hand tear lines was on the order of a 1/4 inch with it being thought that 1/16 inch was the lower desired limit. We have now determined that in the other applications referred to above it is desirable to have a fine grid size of hand-tear lines on the order of less than a 1/16 inch and particularly 1/32 inch or less.